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General Information about the RMS Program

Present Research Areas

The main thrust of current research is on floating offshore wind turbines. Specifically, present work is investigating the potential for reducing the cost of the buoyant hull supporting the wind turbine tower by substantially reducing the required rotational stiffness (roll or pitch) of the structure. This work includes theoretical developments, development of numerical tools, development of control systems including statistical investigations of the behavior of these highly compiant floating structures. Present work primarily funded by the National Science Foundation, Division of Chemical, Bioengineering, Environmental and Transport Systems, CBET-1133682 and CBET-1217253.

General Research Problems and Interests

RMS research interests were often motivated by specific offshore structural concepts. These concepts vary greatly with the properties of the oil/gas field to be developed--most particularly with its water depth. Applications have included oil drilling and production facilities in water depths ranging from 50 meters to more than 2 km. The trend however is ever deeper: exploratory drilling has been performed, from ships, at depths exceeding 3 km. Resulting structural concepts range from familiar rigid piled steel frames ("jackets"), to massive "gravity-based" concrete structures, and more recently to novel, tethered floating structures like TLP's, Spars, and production ships.

Technical challenges for these offshore structures include a number of nonlinear mechanisms. The hydrodynamic forces on these structures are complex nonlinear transformations of the random wave elevation history and current speed. The structure itself may also behave in nonlinear ways, especially under extreme conditions that challenge the safety of the facility. Examples include the restoring forces of the mooring lines under large deformations, and the material and geometric nonlinearities of the jacket braces under severe wave or seismic conditions. The complex fluid-structure interactions of large-body structures in high, nonlinear waves are imperfectly understood and under continuing development; large laboratory tests of proposed designs are common. Our contributions have included procedures for the analysis of model test and, more recently, field data from such structures. These procedures can be used to suggest important combinations of wave and current parameters for use in designing these (expensive) wave tank experiments.

Related Topics of Structural Reliability Research

Because these marine facilities are large investments--construction and installation costs for deep-water platforms may range into the billions of dollars--the offshore industry is ready to study their reliability with care. It is often more prepared than the building or bridge industry to invest in new technology. One result is the possibility of transferring our offshore structural technology into other fields of structural engineering. The bridge and building fields are moving rapidly into the widespread use of nonlinear structural analysis for seismic loadings; the offshore industry pioneered it and codified it in 1980. We use today a dynamic structural analysis code first developed for offshore steel jacket structures, but we apply it both to such structures and to buildings. Probabilistic nonlinear "hazard" analysis procedures, originally developed at Stanford for use on steel jackets, are now being adapted for use on buildings under seismic loading.

Other research projects within RMS studied the reliability of wind turbines--primarily against fatigue failure during its millions of revolutions--and of buildings against seismic threats. The common theme has been to assess the reliability of various engineered structures in uncertain load environments, and to design to maximize this reliability.

Historical Background

The Reliability of Marine Structures Program at Stanford University was a graduate research program within the Civil Engineering Department The program investigated Marine, Seismic and Wind-energy related technologies from 1988 until 2002 when the departure of Dr Steve Winterstein prompted Professor Allin Cornell to disconue the marine-related aspects of the program.

The Reliability of Marine Structures (RMS) Program combined post-M.S. graduate study and basic research in structural reliability applications. These applications ranged across a spectrum of topics, from the modelling of joint ocean environmental processes (wind-wave-current), through the modelling and analysis of the resulting hydrodynamic loads and gross responses, to the development of probability-based design codes.

This research work was funded both by federal sponsors, such as the Office of Naval Research and the National Science Foundation, and by industry affiliate sponsors. RMS sponsors from the oil industry included AGIP, Amoco, British Petroleum, Chevron, Exxon, Mobil, Norsk Hydro, Saga, Shell, Statoil, and Texaco. Other industry sponsors (American Bureau of Shipping, Det Norske Veritas) focused on analysis and design rules for various components of ships.

The RMS program generally included 6-8 Ph.D. students at any one time. For the benefit of the group, extended visits were made by experienced research workers in offshore structural engineering. Some were academics, but most came from research groups within the industry itself.

Managers in the industry are currently exploring new ways to work with universities to "outsource" research and technology development, just as universities are being encouraged to look beyond the federal government to industry for research and student support funding. It is anticipated that the opportunities for interesting, educational, and useful academic research in this field will continue for the foreseeable future.

Consulting Services

Professor Bert Sweetman also provides engineering services through his consulting company, Ocean Structure Dynamcs, LLC. Ocean Structure Dynamics provides specialized consulting services in novel application of theoretical engineering methods to offshore structures. Much of this work is application of random vibration theory to predict structural response to irregular excitation associated with wind, waves and currents.

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